Various studies have shown that plate-making for computer-to-plate (CTP) systems have greatly advanced in recent years. Of these studies, lithographic printing plate precursors capable of being mounted on a printing press without undergoing a development process by a special processor after exposure to effect printing are studied for the purpose of further rationalization of the process and solution of the problems of discarding of waste solution, and various methods are suggested.
As one method of omitting a development process by a special processor, a method of mounting an exposed printing plate precursor on the cylinder of a printing press, and removing a non-image area of the printing plate precursor by supplying a fountain solution and ink with revolving the cylinder which is called on-press development is known. That is, this is a method of mounting a lithographic printing plate precursor on a printing press after exposure as it is and terminating a development process in a usual printing process.
A lithographic printing plate precursor suited for on-press development is required to have a photosensitive layer soluble in a fountain solution and an ink solvent, and daylight handling property as well, since a printing plate precursor is development processed on a printing press put in a bright room.
For example, a lithographic printing plate precursor comprising a hydrophilic support having provided thereon a photosensitive layer containing a hydrophilic binder polymer having dispersed therein thermoplastic hydrophobic polymer fine particles is disclosed in Japanese Patent 2938397. There is disclosed in the same patent that after an image is formed by coalescing the thermoplastic hydrophobic polymer fine particles by heat by infrared laser exposure in the lithographic printing plate precursor, the printing plate is mounted on the cylinder of a printing press, and on-press development can be effected with a fountain solution and/or ink. Further, JP-A-9-127683 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) and WO 99/10186 also disclose a method of making a printing plate by on-press development after coalescing thermoplastic fine particles by heat. However, there is a problem in these methods of making images only by simple coalescence of fine particles by heating that sensitivity is low and high press life can be obtained with difficulty.